The 17056 is used by state and federal Department of Transportation (DOT) agencies to monitor the water content and state (liquid vs. ice) underneath the highway. Three rods emanates from the probe's head at right angles. This construction allows the probe to be installed in a highway bed after the highway has been built. To install, a core is drilled into the highway. The probe is "dangled" into the hole by its cable, and then the hole is backfilled. Some states actually lower the acceptable weight limits for trucks during spring thaw in an attempt to prolong the life of the highway.
The "-L" on a product model indicates that the cable length is specified at the time of order.